Sherrington has demonstrated that the setting of skeletal muscles in opposed groups about a joint or system of joints--as in flexors and extensors--is associated with an internal organization of the central nervous system that provides for relaxation of one group of the opposed muscles when the other group is made to contract. This “reciprocal innervation of antagonistic muscles,” as Sherrington has called it,[26] is thus a device for orderly action in the body. As the above description has shown, there are peripheral oppositions in the viscera corresponding to the oppositions between flexor and extensor muscles. In all probability these opposed innervations of the viscera have counterparts in the organization of neurones in the central nervous system. Sherrington has noticed, and I can confirm the observation, that even though the sympathetic supply to the eye is severed and is therefore incapable of causing dilation of the pupil, nevertheless the pupil dilates in a paroxysm of anger--due, no doubt (because the response is too rapid to be mediated by the blood stream), to central inhibition of the cranial nerve supply to the constrictor muscles--i. e., an inhibition of the muscles which naturally oppose the dilator action of the sympathetic. Pain, the major emotions--fear and rage--and also intense excitement, are manifested in the activities of the sympathetic division. When in these states impulses rush out over the neurones of this division they produce all the changes typical of sympathetic excitation, such as dilating the pupils, inhibiting digestion, causing pallor, accelerating the heart, and various other well-known effects. The impulses of the sympathetic neurones, as indicated by their dominance over the digestive process, are capable of readily overwhelming the conditions established by neurones of the cranial division of the autonomic system. Neurones of the Sympathetic Division and Adrenal Secretion Have the Same Action Lying anterior to each kidney is a small body--the adrenal gland. It is composed of an external portion or cortex, and a central portion or medulla. From the medulla can be extracted a substance, called variously suprarenin, adrenin, epinephrin or “adrenalin,”[*] which, in extraordinarily minute amounts, affects the structures innervated by the sympathetic division of the autonomic system precisely as if they were receiving nervous impulses. For example, when adrenin is injected into the blood, it will cause pupils to dilate, hairs to stand erect, blood vessels to be constricted, the activities of the alimentary canal to be inhibited, and sugar to be liberated from the liver. These effects are not produced by action of the substance on the central nervous system, but by direct action on the organ itself.[27] And the effects occur even after the structures have been removed from the body and kept alive artificially.